Oxygen radicals, generation from

The ultimate fate of the oxygen-centered radicals generated from alkyl hydroperoxides depends on the decomposition environment. In vinyl monomers, hydroperoxides can be used as efficient sources of free radicals because vinyl monomers generally are efficient radical scavengers which effectively suppress induced decomposition. When induced decomposition occurs, the hydroperoxide is decomposed with no net increase of radicals in the system (see eqs. 8, 9, and 10). Hydroperoxides usually are not effective free-radical initiators since radical-induced decompositions significantly decrease the efficiency of radical generation. Thermal decomposition-rate studies in dilute solutions show that alkyl hydroperoxides have 10-h HLTs of 133—172°C. 

A possible mechanism for the formation of the furanones 6 and 7 is illustrated in Scheme 2. The initial alkoxy radical generated from the alcohol 5 and lead tetraacetate (LTA) undergoes /3-scission to produce the acyl radical intermediate 9. Subsequent cyclization to 10 proceeds through attack of the radical at the carbonyl oxygen. The resulting Pb(IV) intermediate 11 finally collapses via the reductive... 

Alkyl radicals generated from azoalkanes as in (7) react with oxygen added to argon matrices giving alkylperoxy radicals. In this manner radicals... 

Entry 11 involves generation and cyclization of an alkoxymethyl radical from a selenide. The cyclization mode is the anticipated 5-exo with a cis ring juncture. This is a case in which the electronic characteristics of the radical are not particularly favorable (ERG oxygen in the radical), but cyclization nevertheless proceeds readily. The reaction in Entry 12 was used to prepare a precursor of epibatidine. Entry 13 shows a 6-endo cyclization that is favored by steric factors. The 6-endo cyclization is also favored with a tetrahydropyranyloxy substituent in place of the ester, indicating that the electronic effect is not important. Entries 14 to 16 involve acyl radicals generated from selenides. The preferred 6-endo cyclization in Entry 15 is thought to be due to the preference for the less-substituted end of the double bond. Entry 17 is an example of a 5-exo-dig cyclization. 

Calcium oxalate monohydrate responsible for the formation of most kidney stones significantly increased mitochondrial superoxide production in renal epithelial cells [42], Recombinant human interleukin IL-(3 induced oxygen radical generation in alveolar epithelial cells, which was suppressed by mitochondrial inhibitors 4 -hydroxy-3 -methoxyacetophe-none and diphenylene iodonium [43]. Espositio et al. [44] found that mitochondrial oxygen radical formation depended on the expression of adenine nucleotide translocator Anti. Correspondingly, mitochondria from skeletal muscle, heart, and brain from the Antl-deficient mice sharply increased the production of hydrogen peroxide. 

Thus, oxygen radical production by leukocytes can be responsible for cancer development. However, the levels of leukocyte oxygen radical generation depend on the type of cancer. For example, PMNs and monocytes from peripheral blood of patients with lung cancer produced a diminished amount of superoxide [169], Timoshenko et al. [170] observed the reduction of superoxide production in bronchial carcinoma patients after the incubation of neutrophils with concanavalin A or human lectin, while neutrophils from breast cancer patients exhibited no change in their activity. Chemotherapy of lung and colorectal carcinoma patients also reduced neutrophil superoxide production. Human ALL and AML cells produced, as a rule, the diminished amounts of superoxide in response to PMA or FMLP [171], On the other hand total SOD activity was enhanced in AML cells but diminished in ALL cells, while MnSOD in AML cells was very low. It has been proposed that decreased superoxide production may be responsible for susceptibility to infections in cancer patients. 

CASRN 56-40-6 molecular formula C2H5NO2 FW 75.07 Chemical/Physical Products identified from the oxidation of glycine and OH radicals (generated from H2O2/UV) in oxygenated water were oxalic acid, formic acid, and ammonium ions. In oxygen-free water, oxalic and formic acids were not produced, i.e., glycine oxidized directly to ammonium ions. The rate constant for the reaction of OH radicals with the zwitterion ion is 1.7 X 10 /M-sec and with the anionic form is 1.9 x 10 /M-sec (Vel Leitner et al., 2002). 

SCHEME 10. Preparation of hydroperoxides via oxygenation of carbon radicals generated from iV-hydroxypyridine-2-thione esters as radical precursors... 

A new process for the homolytic acylation of protonated heteroaromatic bases has been developed by Minisci et al. An A-oxyl radical generated from iV-hydroxyphthalimide by oxygen and Co(ll) abstracts a hydrogen atom from an aldehyde. The resulting nucleophilic acyl radical adds to the heterocycle which is then rearomatized via a chain process. Under these conditions, quinoline and benzaldehyde afford three products (Equation 108) <2003JHC325>. A similar reaction with 4-cyanopyridine gives 2-benzoyl-4-cyanopyridine in 96% yield. 

Alkyl radicals generated from the reduction of halides or sulfones with Sml2 have been successfully exploited in intramolecular additions to alkenes that result in the generation of a variety of functionalised small carbocyclic and heterocyclic ring systems. Substrates containing an oxygen atom within the... 

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